Abstract:

The invention relates to a respiratory gas supply circuit for an aircraft
carrying passengers, comprising a pressurized source of respiratory gas
(R1, R2) and a supply line (2, 3), said circuit further comprising on
said supply line a regulating device (12, 30) for controlling the supply
in respiratory gas to said passengers, wherein said regulating device
further comprises an electro-valve (12) controlled by a pulse width
modulation signal provided by an electronic unit (20).

Claims:

1. A respiratory gas supply circuit for an aircraft carrying passengers,
comprising a pressurized source of breathable gas and a supply line, said
circuit further comprising on said supply line a regulating device for
controlling the supply in breathable gas to a plurality of respiratory
masks for said passengers,wherein said regulating device further
comprises an electro-valve controlled by a pulse width modulation signal
provided by an electronic unit.

2. A circuit according to claim 1, wherein the electro-valve is a solenoid
valve.

3. A circuit according to claim 1, wherein the solenoid valve is a two
position on/off solenoid valve, with a variable duty ratio.

4. A circuit according to claim 1, further comprising a first pressure
sensor provided in the cabin of the aircraft, to supply a first pressure
signal to the electronic unit for elaborating a set point to control the
electro-valve.

5. A circuit according to claim 1, wherein a second pressure sensor is
provided on the supply line downstream the regulating device, to supply a
second pressure signal to the electronic unit corresponding to the
regulated pressure.

6. A circuit according to claim 4, wherein the electronic unit compares
the set point to the regulated pressure to elaborate the pulse width
modulation signal.

7. A circuit according to claim 6, wherein the electronic device comprises
a PID module to elaborate the pulse width modulation signal.

8. A circuit according to claim 3, wherein the electro-valve is provided
on the supply line to either switch on or off the supply in breathable
gas in response to the pulse width modulation signal provided by the
electronic unit.

9. A circuit according to claim 3, wherein the inlet of the solenoid valve
is connected to the pressurized source of respiratory gas, said circuit
further comprising a piston movable between a first position wherein the
supply line is open and a second position wherein the supply line is
closed, said piston being movable in response to the outlet pressure of
the two position on/off solenoid valve.

Description:

[0001]The present invention relates to a respiratory gas supply circuit
for protecting the passengers of an aircraft against the risks associated
with depressurization at high altitude and/or the occurrence of smoke in
the cockpit.

[0002]To ensure the safety of the passengers in case of a depressurization
accident or the occurrence of smoke in the aircraft, aviation regulations
require on board all airliners a safety oxygen supply circuit able to
supply each passenger with an oxygen flow rate function of the aircraft
altitude.

[0003]In other words, the source of gas under pressure must be capable of
instantly delivering oxygen or air greatly enriched in oxygen at a
pressure sufficient for feeding the passengers.

[0004]Current systems are mainly pneumatic systems, regulating the
pressure of the supplied oxygen thanks to a reducing valve operating as a
function of the cabin pressure, or cabin altitude. By cabin altitude, one
may understand the altitude corresponding to the pressurized atmosphere
maintained within the cabin. This value is different than the aircraft
altitude which is its actual physical altitude.

[0005]Such a pneumatic system is known from FR2646780. The described
supply circuit allows an altitude-dependent regulation of the flow of
respiratory gas fed to passengers through an orifice provided on
breathing masks and comprises high-pressure oxygen reservoirs, a pressure
regulator, and a valve. The valve is an altitude-dependent valve with an
on/off functioning and does not provide any regulating function. The
regulation of the oxygen flow is ensured individually for each cluster of
breathing masks thanks to regulation means comprising an altimetric cell
acting on a movable leak proof membrane.

[0006]The known pneumatic supply circuits generally lack a feedback loop,
and are oversized as far too much oxygen is supplied to the mask wearers
to ensure that the oxygen flow rate matches the regulatory minimums.

[0007]An object of the present invention is to provide an improved
respiratory gas supply circuit that is simple, reliable and does not
present the drawbacks from the known systems. An additional object of the
present invention is to provide a supply circuit with a feedback loop
that optimizes the need in respiratory gas and thus limit the onboard
mass of breathing gas.

[0008]To this end, there is provided a respiratory gas supply circuit for
an aircraft carrying passengers as claimed in claim 1.

[0009]The pulse width modulation (PWM) signal allows an easy piloting of
the electro valve, which is a reliable regulating device.

[0010]The above features, and others, will be better understood on reading
the following description of particular embodiments, given as
non-limiting examples. The description refers to the accompanying
drawing.

[0011]FIG. 1 is a simplified view of a respiratory gas supply circuit for
an aircraft carrying passengers according to a first embodiment of the
invention;

[0012]FIG. 2 is a simplified view of a respiratory gas supply circuit for
an aircraft carrying passengers according to a second embodiment of the
invention, and;

[0014]As seen on FIG. 1, the supply circuit according to the invention
comprises the hereafter elements. A source of pressurized respiratory or
breathable gas, here a couple of oxygen tanks R1 and R2 each comprising a
reducing valve on their respective outlet, is provided to deliver through
a supply line 2 a respiratory gas to the passengers of the aircraft.
Other sources of pressurized breathable gas may be used in the supply
circuit according to the invention. A plurality of secondary feedlines 3
is connected between supply line 2 and clusters 4 of respiratory masks 9.
Each cluster 4 of masks 9 may be provided in an enclosure 5 placed over
the passengers' seats. The enclosure 5 may comprise a junction 11 of
feedline 3 into said box, a door 6 articulated around hinge 7 (and seen
closed in the central cluster, and open in the right hand side cluster),
and a connecting casing 8 that connects feedline 3 with the respiratory
masks 9 thanks to flexible pipes 10. The breathable gas is generally
supplied to its wearer through an orifice within said mask.

[0015]A regulating device 12 is further provided, for example within
enclosure 5, to control the supply in respiratory gas to the masks and
the passengers. In the supply circuit according to the first
implementation of the invention, the regulating device 12 comprises an
electro-valve controlled by a pulse with modulation signal provided by an
electronic unit.

[0016]Pulse width modulation (PWM) is a powerful technique for controlling
analog circuits with a microprocessor's (CPU) digital outputs. PWM is
employed in a wide variety of applications, ranging from measurement and
communications to power control and conversion. Pulse-width modulation
control works by switching the power supplied to the electro-valve on and
off very rapidly and at a varying frequency. A DC voltage is converted to
a square-wave signal, alternating between fully on (e.g. nearly 12V or
18V) and zero, giving the valve a series of power "kicks" of varying
length. An example of such a signal is shown in FIG. 3.

[0017]To that effect an electronic unit 20, or CPU, is provided to
elaborate the PWM signal sent to electro-valve 12, as seen in doted lines
for both clusters 4 of masks. A first pressure sensor 25 is provided in
the cabin of the aircraft to supply a first pressure signal to the CPU 20
for elaborating a set point to control the electro-valve 12. Pressure
sensor 25 measures the cabin pressure, and allows the supply in
respiratory gas as a function of the cabin altitude, so that the
regulations oxygen supply curves are ensured. The pressure sensor 25 may
be one of the pressure sensors available in the aircraft, its value being
available upon connection to the aircraft bus. In order to ensure a
reliable reading of the pressure independent of the aircraft bus system,
the circuit according to the invention may be provided with its own
pressure sensor, i.e. a sensor 25 is provided for each electronic unit
20.

[0018]A second pressure sensor 15 is provided on the supply line
downstream the regulating device 12, i.e. in the example of FIG. 1 within
the enclosure 5 between electro-valve 12 output and connecting casing 8,
to supply a second pressure signal to the CPU 20 that corresponds to the
regulated pressure. Second pressure sensor 15 allows a feedback loop to
ensure that the right supply in oxygen follows the demand from the
passengers when wearing the masks.

[0019]To that effect, the electronic unit 20 compares the set point to the
regulated pressure, i.e. the value of sensor 15 to elaborate the PWM
signal.

[0020]A PID module (proportional, integral, derivative) may be comprised
within electronic unit 20 to elaborate the PWM signal from the comparison
of the set point and the regulated pressure.

[0021]In an additional embodiment, electro-valve 12 is a solenoid valve.
More precisely, in a preferred embodiment, electro-valve 12 is a two
position on/off solenoid valve, with a variable duty ratio. Such a valve
is particularly suited to be driven by the PWM signal sent by CPU 20. The
valve may also be a piezo electric valve. In the first implementation of
the supply circuit according to the invention, valve 12 is provided on
the supply line, and directly opens and cuts off the supply in
respiratory gas. More precisely, in the illustration of FIG. 1, valve 12
is provided within the box 5 between junction 11 and connecting casing 8.

[0022]The first implementation of the invention is particularly well
suited to drive a cluster of masks locally through the regulating device
12. Each cluster 4 is attached to its own regulating device. This ensures
that if for some reasons one cluster fails, its does not affect the other
clusters that carry on the supply in respiratory gas.

[0023]In the first implementation, the electro-valve 12 directly drives
the supply in breathable gas as valve 12 is located on supply line 3.

[0024]The regulating means or the pressure sensor 15 may be advantageously
located close to the cluster of masks. By a close location, one may
understand a location on the supply line wherein the pressure loss
between each mask and the regulating device, or the pressure sensor
respectively, is negligible.

[0025]The second implementation of the supply circuit according to the
invention is illustrated in FIG. 2. Unless written otherwise, the same
numbers refer to the same parts.

[0026]The regulating device comprises a flow amplifier 30 provided on the
supply line 2 connecting a source of pressurized breathable gas (not
shown) to a plurality of respiratory masks 9 provided for example within
an enclosure 5 as described for the previous embodiment. The flow
amplifier 30 further comprises a piston 32, e.g. an annular piston,
subjected to the pressure difference between the ambient pressure and the
pressure that exists inside a piston chamber 34. An electro-valve 12,
e.g. specifically a solenoid valve, serves to connect the piston chamber
34 to the pressurized respiratory gas through pipe 122. Chamber 34 may
also be connected to the ambient pressure in the cabin through pipe 123.

[0027]Electro-valve 12 thus serves to vary the pressure within chamber 34
so that piston 32 is movable between a first position wherein the supply
line is open (piston 32 is kept away from supply line 2 inner section)
and a second position wherein the supply line is closed (piston is pushed
to close an inner section of supply line 2). Piston 32 is movable in
response to the outlet pressure of the two positions on/off solenoid
valve 12, its inlet being connected to the source of pressurized
respiratory gas.

[0028]When the piston chamber 34 is connected to the cabin ambient
pressure, i.e. solenoid valve 12 is off, and the pressure in chamber 34
is maintained to the cabin ambient pressure thanks to pipe 123, a spring
38 holds piston 32 in a position away from closing supply line 2. When
solenoid valve 12 is on, chamber 34 is connected to the pressurized
source of respiratory gas through pipe 122. A narrow section may be
provided on pipe 123 so that its section is insufficient to lower the
pressure in chamber 34 when solenoid valve 12 is on.

[0029]Electro-valve 12 is controlled through CPU 20 that sends a PWD
signal that can be elaborated thanks to the first pressure sensor 25
provided in the cabin of the aircraft and/or thanks to the second
pressure sensor 15 provided downstream the regulating device as described
before.

[0030]The second implementation of the invention allows to drive a large
number of masks through the regulating device thanks to the flow
amplifier 30.

[0031]In the second implementation, as the demand in breathable gas may be
larger and the pressure loses along supply line 3 larger, a flow
amplifier 30 is required. The supply in breathable gas is driven
indirectly by valve 12 as a result of valve 12 piloting piston 32.

[0032]The invention allows to control the volume of breathable gas
supplied to the masks. The successive opening and closing cycles of the
regulating means lead to a controlled average volume or "integrated"
volume of breathable gas downstream the regulating means. The average
volume creates a pressure P that is measured thanks to pressure sensor
15. Based on the cabin altitude, a breathable gas must be fed to the mask
at a pressure set point value. The PWM signal is elaborated by the
electronic unit to pilot the regulating means to deliver said breathable
gas at said pressure set point value.

[0033]The time between pulses and/or the length of each pulse may vary to
ensure the right volume of breathable gas fed to the masks, based on the
feedback loop and the set point.

[0034]The respiratory gas supply circuit according to the invention is
particularly well suited to be associated to a rebreathing bag as known
from US 2003,101,997. Such a document discloses a respiratory mask for
protecting passengers of an airplane against depressurization of an
airplane cabin at high altitude, the mask being provided on a respiratory
supply circuit comprising a feed control unit for supplying an adjustable
continuous flow rate to a general pipe from a source of respiratory gas
under pressure. The masks are further connected to said general pipe via
a flexible economizer bag. Furthermore, a flexible re-breathing bag is
connected to each of said mask by means enabling gas to enter freely into
the flexible re-breathing bag from the mask and retarding re-breathing
from said flexible re-breathing bag after beginning of breathing in by
one of said passengers bearing the mask. The re-breathing bag has
preferable a volume when inflated such that it is capable to store only
an initial fraction of the gas breathed out on each exhalation by the
passenger wearing the mask. The control unit of US 2003,101,997 further
has means for regulating the flow rate of additional oxygen delivered to
said pipe responsive to ambient pressure to which the mask wearers are
subjected in order to limit said flow rate to a fraction only of the flow
rate that would be necessary in the absence of re-breathing.